1. Field of the Invention
The present invention generally relates to a filter screen assembly, and more specifically, a filter screen assembly for a dishwasher that filters soil from wash or rinse water and is automatically backflushed by drain water.
2. Description of Related Art
Domestic or household dishwashers generally consist of an enclosed cabinet having a bottom hinged door at the front of the cabinet for closing off an otherwise sealed washing chamber or tub. Dishes are placed on upper and lower racks which are arranged to slide or roll in and out of the tub when the door is open. The dishwashers typically have a rotating lower wash arm which rotates and carries a number of spray openings which direct water upward as the arm rotates to spray all of the dishes in the tub. Additionally, some dishwashers have an upper wash arm located above the lower rack and below the upper rack to provide additional washing ability. Furthermore, some dishwashers have an upper wash arm beneath the top wall of the tub to spray water down on all the dishes in the tub.
The dishwashers typically operate with alternating wash and rinse cycles in which the wash cycle is distinguished only by length of time and the fact that detergent has been added to the water. During each cycle, the water is drawn from a sump at the bottom of the tub and passes through a pump to the wash arms. The water passes over the dishes in the racks and returns to the sump. After each wash or rinse cycle is a drain cycle for removing the fluid within the sump so that it can receive fresh water.
A problem with all types of dishwashers is handling soil particles removed from the dishes being washed. As the soil particles are washed off the dishes, they pass into the water in the sump, are drawn into the pump with the water, and are recirculated through the wash arms. Therefore, the soil particles can be redeposited on the very dishes from which they were removed. Some soil particles are removed by a screen in the sump. Most of the soil particles pass through the screen, however, because the screen must be relatively coarse so that it does not become clogged.
In the case of dishwashers having separate drain and recirculation pumps, the solution to this problem has been to provide a collector or filter screen arranged such that the water passes through the filter screen in the recirculating cycles prior to entering the recirculation pump to remove the soil particles. The filter screen is automatically cleaned by water going to the drain from the drain pump during the drain cycle.
In the case of dishwashers having a single unidirectional pump, the solution to this problem has been to provide the pump with a macerator or cutting blade to break up the soil particles as they are recirculated until they become sufficiently fine to be less likely to be redeposited on the dishes. Alternatively, a filter screen is provided between the pump and the upper spray arm so that filtered water will wash or rinse any soil particles off the dishes even if such soil particles have been redeposited on the dishes by the lower spray arm. The filter screen is automatically cleaned by water going to the drain from the pump during the drain cycle.